Process for producing dental devices

ABSTRACT

A process for producing dental devices such as teeth is disclosed. Specifically, a process for producing gold dental devices, such as gold denture teeth, is disclosed. The process includes the production of an injection mold based on an impression or mold of a target tooth. The injection mold can then be utilized to produce a hardened polymeric precursor of the product device. In particular, a hardened precursor can be produced from pure polypropylene. The precursor can be used as a model to produce an investment casting mold. The desired product material, for example a gold alloy, can then be cast in the investment casting mold by methods known in the art to produce the final product.

BACKGROUND OF THE INVENTION

[0001] Artificial gold dental teeth have been constructed and produced for the dental industry for many years. Historically, the wearing of gold teeth could display wealth and dates back thousands of years. There are currently two types of gold teeth that are available. These types are fixed and removable. Individuals who want the look of gold in their mouth will sometimes have a fixed thin gold shell crown permanently inserted over an existing anterior (front) tooth by a dentist. Those who wear removable dental prosthetics can obtain their choice of gold crowns by visiting their dentist and choosing one of the many designs of gold shell crowns currently available on the marketplace. In addition to the ornamental desires of the patient, gold teeth can be more readily accepted by the oral tissue than other types of dental alloys and sometimes are recommended by the doctor.

[0002] Early techniques for producing artificial gold teeth, such as denture teeth, required stamping a flat tooth pattern from a sheet of 22 karat gold. This pattern would then be formed around a tooth mold and then soldered together where the sides met the lingual surface of the tooth (for purposes of the application, the lingual surface of the tooth is intended to refer additionally to back or palatal surface of teeth). In order to remove the gold shell crown from the forming mold, the lingual surface had to be flat and parallel for easy removal. The soldering of the sides to the lingual surface of the tooth formed sharp 45-degree angles at the junctions.

[0003] These earlier methods of producing gold denture teeth created a product that did not resemble a natural tooth shape. For example, the square edged 45-degree soldered junctions did not resemble the natural rounded edges found on natural teeth.

[0004] In more recent times, investment casting processes have been utilized for casting dental alloys in the production of various dental devices, including dental crowns and artificial teeth. Investment casting is a known option for producing accurate reproductions of small, detailed shapes, such as is found in the dental industry. Within the dental industry, the investment casting process is commonly known as the “lost wax” method. In this process, a wax model of the target tooth can be hand crafted. The wax model can then be used in an investment casting procedure. Artificial teeth produced by the lost wax method tend to have surface flaws when produced in an unsanitary environment that could contaminate the wax patterns. Additionally, since these patterns were hand waxed, the wall thickness of the wax model directly affected the amount of raw material required to produce the final product. This can particularly be a problem when casting precious metals, such as gold alloys. Hand waxing of denture teeth was also time consuming and costly to the dental profession.

[0005] Additionally, prior art artificial gold denture teeth were constructed with an indentation or a groove on the labial surface near the top of the tooth. The short remaining surface on the labial side of the tooth from the indentation to the very top edge is called the “collar” of the tooth. The collar edge is used to anchor the tooth into the denture base for retention. Denture teeth vary in sizes. The physical length of a denture tooth is determined by measuring the distance from the bottom of the tooth (incisal or biting edge) up to the indentation. If, subsequent to manufacture, the tooth has to be adjusted up or down for any reason (for example, to match in height the other teeth on the denture) this collar line could become visible. A visible collar line on the tooth could be a detriment to the aesthetic appeal of the gold tooth.

[0006] Thus a need exists to produce a high quality dental device, such as a gold denture tooth, which closely resembles a natural tooth in shape and has no seams, flaws or markings which could detract from the aesthetic quality of the device. Specifically, the present invention will produce a gold denture tooth that has a facial surface without an indention or collar area. The removal of the indention makes it possible to increase or decrease the physical appearance of the tooth as needed without detriment to the aesthetic appeal of the gold tooth. Additionally, a need exists to produce such a dental device while minimizing manufacturing costs. Tooth designs, which may be produced by the process of the present invention, have been disclosed in Design patent application No. 29/131,167.

SUMMARY OF THE INVENTION

[0007] In general, the process of the present invention is an improved process for producing dental devices. Specifically, the present invention is directed to an improved process for producing unitary dental devices, such as denture teeth or crowns. More specifically, the present invention is directed to producing gold artificial teeth by an improved investment casting method.

[0008] In order to produce the dental devices of the present invention, a mold or impression of a target tooth can be provided. Using this mold or impression as a guide, an injection mold can be formed. The injection mold can define a cavity of the shape of the desired dental device, such as, for example, a tooth or a crown, and can include an insert which can be placed within the cavity when assembling the injection molding die to be utilized during the injection molding process.

[0009] Once the injection mold has been created and assembled, a formable material can be injected into the mold. For instance, a polymeric material may be injected into the mold. The polymeric material may be a thermoplastic material, although certain thermoset materials may also be injection molded. The polymeric material may be molten in order to facilitate the injection molding process. The material can then be cured or set in order to form a hardened polymeric precursor having the general shape of the dental device. In an alternative embodiment, the injection mold can define more than one cavity in order to form more than one precursor at a time.

[0010] In general, the material can be any suitable polymeric material which may be injection molded. For example, the polymeric material can be a thermoplastic material such as a polyolefin. In certain embodiments, the polymeric material can be a polypropylene, a polyethylene, or a copolymer of the two. Of particular importance to the process, the inventors have discovered that the polymeric material chosen in forming the injection molded thermoplastic precursor can improve the characteristics of the final product. In one embodiment of the present invention, the inventors have discovered that use of pure polypropylene as the material for a tooth precursor can allow for the formation of a product gold tooth with fewer surface flaws. Surface flaws can include flaws such as pitting, for example.

[0011] The precursor thus produced can then be used as a pattern for producing an investment casting mold. In an alternative embodiment, an injection molded polymeric precursor can be provided preformed to the maker of the investment cast. The investment casting mold can include only one precursor within it, or alternatively can be formed to include several precursors in order to mold more than one device at a time.

[0012] An investment casting mold is generally formed by surrounding one or more precursors by a liquid casting material which is then set to form the mold. The polymeric precursor material can be removed from the interior of the investment casting mold after the liquid casting material has hard set. In one embodiment of the present invention, this can be accomplished by burning out the polymeric material from the interior of the cast. For example, certain thermoplastic precursor materials can be burned out of the solid investment mold at a temperature of from about 1200° F. to about 1300° F., particularly at a temperature of from about 1225° F. to about 1275° F., more particularly at a temperature of about 1250° F.

[0013] After the investment casting mold has been prepared, a molten metal can be cast into the shape of the desired dental device. Specifically, a precious metal can be cast. More specifically a gold alloy such as, for example, a 22 karat gold, a white gold or a coin gold may be cast in the mold.

[0014] When a gold tooth or gold crown is formed by the process of the present invention, the product can have a thin wall. For example, a tooth formed by the disclosed process can have a wall thickness of from about 0.0010 to about 0.0011 inches.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

[0016]FIG. 1 is a perspective view of an artificial denture tooth made in accordance with the present invention.

[0017]FIG. 2 is a cutaway view of an injection molding die suitable for use in the process of the present invention.

[0018]FIG. 3 is an illustration of four polymeric precursors for denture teeth produced by the injection molding process of the present invention.

[0019]FIG. 4 is an illustration of several denture tooth precursors attached to an investment tree in preparation for preparing an investment casting mold.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary construction.

[0021] In general, the current invention is directed toward a process for producing dental devices. In particular, the current invention provides a process for producing dental devices such as gold crowns and unitary gold teeth, such as denture teeth, through an improved investment casting procedure.

[0022] For purposes of this application, a unitary tooth is defined as a tooth made of a single piece of a material, having no seams or joints.

[0023]FIG. 1 illustrates a denture tooth 100, which can be produced by the process of the present invention. As shown, tooth 100 includes labial surface 110 and lingual surface 120. Tooth 100 can also include mechanism 130. Mechanism 130 can be, for example, an anchoring mechanism useful for attaching the denture tooth to a denture base.

[0024] As shown, tooth 100 is designed as a central tooth. Alternatively, a tooth produced by the present process could be designed as any desired tooth, such as a lateral tooth, a cuspid, a bicuspid, or a molar tooth.

[0025] Whether producing teeth, crowns, or any other desired dental device, the process of the present invention can begin with a model or impression of the target tooth. In one embodiment of the present invention, an impression or model of a patient's tooth can be supplied to the maker from a dentist, orthodontist, other health care provider, or laboratory.

[0026] Using the model or impression as a guide, a wax pattern of the product can be crafted. For example, a wax model of a hollow denture tooth can be crafted. In one embodiment of the invention, this wax model is hand-crafted. The wax pattern can be altered from the shape of the natural tooth as necessary in order to design the shape of the final product. For example, areas of the tooth which can pose a problem to proper seating of the final product can be adjusted when forming the wax pattern. Additionally, integral components can be included as part of the wax pattern for improved product design. For example, the wax pattern may be formed to include integral components such as sizing mechanisms, spacing mechanisms, or anchoring mechanisms.

[0027] Proper and secure insertion of a dental device into a denture or gum can be an important aspect to be considered when designing the final product. In one possible embodiment of the present invention, in order to assure correct product insertion into a denture or gum, tabs or posts can be crafted as part of the initial wax pattern. Such tabs or posts can be used as, for example, a means of attachment, such as an anchor, allowing a tooth to be firmly affixed to a denture.

[0028] As previously stated, a similarly formed wax pattern has been used in the past in a conventional lost wax casting procedure to produce dental devices. When casting precious metals, such as a gold alloy, however, it is preferred to contain costs. One possible method of containing costs is to limit the amount of gold required in forming the final product. This can be accomplished by limiting the wall thickness of the pattern used to produce the investment casting mold. A thin walled pattern can form a thin walled mold in an investment cast and therefore limit casting material necessary to form the final product.

[0029] As such, the inventors have discovered that an injection molding process can be combined with the conventional casting process to produce a dental device such as a denture tooth.

[0030] In general, injection molding is a process which involves injecting a measured quantity of a molten material into a die under pressure via a sprue. The sprue includes the aperture as well as any channels the material will pass through within the mold before reaching the mold cavity itself. In the present invention, the die can be utilized to mold a thin-walled precursor of the final product. The thin-walled precursor can then be used to form an investment mold for use in an investment casting procedure.

[0031] In accordance with the present invention, a previously formed wax pattern can be used as a model to produce an injection molding die. The material used to produce the die is not critical, and can be any suitable material. For example, the die may be formed of a metal, such as aluminum, hardened steel or stainless steel, although other materials may also be found to be acceptable.

[0032] A portion of an injection molding die suitable for use in the current invention is illustrated in FIG. 2. As illustrated, the die is a multi-pattern die which would allow for the formation of as many as four precursors at one molding, though this number is not critical to the invention and less or more than four precursors can be molded at one time. The die can alternatively be designed to form only one or any number of precursors at one time.

[0033] As shown, an injection molding die can be a die which includes several separate pieces which are generally treated in a like manner and can then be assembled to form the complete die. The separate pieces which together form the die can be formed all of the same material or, alternatively can be made of different materials. Removal of the precursor from the die after the molding process is complete may be facilitated by a mold formed of more than one piece. A front section 220 and back section (not shown) can be paired during the molding process in order to define at least one cavity 225 within the die. The shape of cavity 225 can be based on the wax model previously discussed. Insert 210 can be placed within cavity 225 allowing for a gap 240 to remain between the wall of cavity 225 and insert 210 when the die is completely assembled.

[0034] The insert 210 of the die may either be one solid piece as shown in FIG. 2, or alternatively may be several pieces which fit together to form the entire insert. Which insert arrangement is preferred can depend on, for example, the shape of the precursor being molded. Whether it is made of one piece or several, insert 210 can be formed to closely mirror the dimensions of the wall of cavity 225 in order that gap 240 be kept small. The width of gap 240 will define the wall thickness of the molded precursor, which forms in gap 240.

[0035] When producing a denture tooth, the wall thickness of the precursor can define the wall thickness of the final product tooth. When precious metals are to be cast to form a product, minimal amounts are preferred in order to minimize costs, yet at the same time strength and durability of the product should be maximized. In general, a gold denture tooth with a wall thickness of about 0.0010 to about 0.0011 inches has been found to adequately meet the desired specifications. The invention is not limited to teeth having a wall thickness within that range, however, as wall thickness of less than 0.0010 inches or more than 0.0011 inches may be employed in the practice of the invention.

[0036] Once the die has been assembled, a formable material can be injected through sprue 230 under pressure in order to ensure a complete fill of gap 240 by the material. The material chosen for the tooth pattern can be any material which can function well in both the injection molding step and the later investment casting step of the process. In order to facilitate the molding process, it may be desirable to use a molten material. Suitable materials have been found to include polymeric materials. Possible polymeric materials in general include moldable thermoplastic as well as moldable thermoset materials.

[0037] In general, thermoplastic polymers are those which can soften upon heating, and can be made to flow when a stress is applied. When cooled again, they can reversibly regain their solid nature. Thermoplastics which can be used in forming the injection molded precursor can include but are not limited to polyolefins. Possible thermoplastic materials which can be used in the process of the present invention can be exemplified by, for example: vinyls, such as polyvinyl chlorides and saran (polyvinylidene chloride); polybutylenes; polyethylenes, including flourocarbons such as tetraflouroethylene (Teflon); acrylics, such as polymethyl methacrylates; polypropylenes; and polycarbonates.

[0038] Thermoset polymers in contrast, are those which form covalent crosslinks between adjacent molecular chains upon heating and do not soften upon subsequent heating. Thermosets may also be injection molded, but curing will usually take place under pressure and higher heating conditions than would a thermoplastic material. Thermosetting polymers include, for example: epoxies, phenolics, polyesters, and silicones.

[0039] Copolymers of various polymeric materials can also be used in the process of the present invention. For example, polyethylene-polypropylene copolymers can be utilized in the process.

[0040] In one particular embodiment of the present invention, pure polypropylene (that is, polypropylene with no added fillers) can be used to form the injection molded precursor. Polypropylene has a glass transition temperature of −4° F. and a melting temperature of 347° F. It is resistant to heat distortion, relatively inexpensive, and chemically inert. It can be obtained under common trade names such as, for example, Pro-fax, Tenite, and Moplen.

[0041] After injection of the polymeric material, the die can be cooled until the molded material is hard set. The amount of time required for curing can depend on the material used as well as other process conditions. When using certain thermoplastic materials, curing can occur within 20 to 30 seconds, or even less in some cases. The die can then be disassembled and the hardened precursor, which can still be attached to the hardened polymeric material which set within the sprue, can be removed from the die.

[0042]FIG. 3 illustrates an example of a mold produced by an injection molding process which includes four tooth precursors 300 a, 300 b, 300 c, and 300 d. Each precursor, such as 300 a, for example, can include anchoring mechanism 320 which can be used to provide secure attachment of the product tooth to a denture device. Note that in this illustrated embodiment, the precursors 300 a-300 d are still attached to the polymeric material which set within the sprue and formed legs 330 a-330 d. It may be convenient to leave the precursors 300 a-300 d attached to the legs 330 a-330 d. For example, leg 330 a could serve as a convenient ‘handle’ for manipulating the precursor 300 a in later process steps.

[0043] Once a hardened polymeric precursor 300 a has been produced, it can be used as a pattern to form an investment casting mold of the final product. In general, investment casting processes are those which use a unitary mold in formation of a product. A unitary mold differs from an injection molding die in that the injection molding die can be made of several different pieces which are joined together to form the complete die. A unitary mold has no joints. Investment casting is preferred in this part of the process of the present invention because it allows the maker to achieve high dimensional accuracy in the small castings being produced.

[0044] In general, an investment casting process involves forming a unitary mold by pouring a liquid slurry around a pattern. After the slurry is set or cured to form a solid cast by, for example, heat, pressure, or a combination of both, the pattern material is removed from the interior of the cast. The product material to be shaped by the mold, usually a molten metal, can then be poured into the mold and cured. After complete curing, the surrounding cast can be removed from the molded product material.

[0045] One possible embodiment of the present invention makes use of an investment tree during the investment casting process. Use of an investment tree can allow more than one precursor to be cast at one time. This in turn provides for a more economical, faster process. For example, up to about fifteen injection molded precursors may be attached to a single investment tree and all cast at one time. The total number of precursors which may be cast at one time can depend on the size of the processing equipment as well as other specifications of the process.

[0046] Referring to FIG. 4, one possible embodiment of an investment tree is illustrated which has several precursors 410 a-410 f attached to it. The investment tree can include a base 400 and one or more runner bars 430. Base 400 incorporates a raised section 440. Base 400 can be constructed of essentially any material which will not melt at the process temperatures. Base 400 may be constructed of, for example, rubber.

[0047] Runner bars 430 are attached to base 400 on the inner raised section 440 of the base. There may be one or more runner bars 430 attached to base 400 depending on the number of precursors 410 a-410 f to be cast at one time. Generally, the runner bars 430 are formed from a material which can later be removed from the interior of the investment casting mold. For example, the runner bars 430 can be formed from a wax, such as paraffin or rope wax and may be attached to the base with a small amount of the heated wax.

[0048] A precursor 410 a, for example, can be attached to a runner bar 430 by use of leg 420 a which can be the same as leg 330 a shown in FIG. 3. Alternatively, precursor 410 a can be attached to a runner bar 430 by any means which prevents damage to the precursor. Leg 420 a can be attached to runner bar 430 by simply employing a small amount of heated wax. Alternatively, the method of attachment can utilize any material which will not interfere with the casting process. More than one precursor may be attached to a runner bar 430 as illustrated in FIG. 4 by precursors 410 a-410 f. Alternatively, only one precursor at a time can be attached if desired.

[0049] Once the precursors 410 a-410 f have been attached to the investment tree, an investment casting mold can be formed. In one possible embodiment for producing an investment casting mold, a ring can be attached to the investment tree base 400. The ring can form a continuous wall around the base 440. The wall height should reach above the height of the precursors attached to the investment tree, but should not come into contact with either the runner bars 430 or the precursors 410 a-410 f. The wall is usually made of a metal, though the material of the wall is not critical to the invention. The wall need only be of a material which will not interfere with the remainder of the investment casting procedure.

[0050] Once the wall is attached to the base 400 of the investment tree, an enclosed ring will be formed with the runner bars 430 and the precursors 410 a-410 f inside. A liquid slurry of an investment compound can then be poured inside the ring, filling the ring to a depth which can completely cover the runner bars and the precursors.

[0051] There are many investment compounds available which may be known to one skilled in the art. One possible investment compound which can be utilized for the process of the present invention is Beauty-Cast which is available from the WhipMix Corporation of Louisville, Ky.

[0052] After pouring, the investment compound can be cured to form a solid investment cast. Curing of the cast may be attained by use of temperature, pressure, or a combination of both. In one possible embodiment of the present invention the entire investment system, including the investment tree with patterns attached, the liquid investment compound, and the encircling ring, can be placed under a pressure of about 30 psi for approximately 30 minutes in order to cure the compound. This process can cure the liquid investment compound and form a solid investment cast inside the encircling ring.

[0053] Alternatively, other methods for curing the liquid investment compound may be utilized. For example, high temperature, different pressures, or different amounts of time at various temperatures and pressures may be employed for curing the compound.

[0054] After the investment compound is completely cured, the base of the investment tree can be removed from the cast. This can be accomplished by merely inverting the now solid cast and removing the base 400 from the solid cast. This can expose a portion of the runner bar where the runner bar 430 was attached to the raised portion of the base 440.

[0055] To complete the investment mold, the precursor material as well as any other material remaining inside the cast, for example, the runner bar material and the leg material, can be removed from the interior of the investment cast. This removal can leave voids within the cast which can form a sprue connected to the unitary molds. A suitable method of removal can be any method in which there is little or no material remaining within the mold which could be a detriment to the casting process.

[0056] One possible method of removal can involve burning out the interior contents of the mold. For example, the interior contents of the mold can be removed by heating the cast to a predetermined burn out temperature and maintaining that temperature until the interior material has been suitably burned away. The required burn out temperature can vary depending on the make-up of the interior contents.

[0057] When a burn-out method is utilized to remove the interior contents of the investment cast mold, it may be desired to slowly heat the investment cast from ambient to the predetermined burn out temperature. For example, an oven containing the cast may be heated at a rate of temperature increase of about 35° F. to about 45° F. per minute. More particularly, an oven containing the cast may be heated at a rate of temperature increase of about 40° F. to about 42° F. per minute. Slow heating of the cast can help to prevent damage to the interior of the cast. For example, if the interior content is heated too quickly during burn out, the precursor material may bubble and damage the interior of the investment cast. Damage to the interior of the investment cast can subsequently damage the final product.

[0058] In one embodiment of the present invention pure polypropylene (that is, polypropylene with no fillers) can be used to form the precursors by means of an injection molding process. In this particular embodiment, burn out temperature can be between about 1200° F. and about 1300° F. Particularly, burnout temperature can be between about 1225° F and about 1275° F. More particularly, burnout temperature can be about 1250° F. Once the oven reaches the burn out temperature, it can be kept at that temperature for a period of time in order to ensure suitable burnout of materials in the cast. For example, when the precursor has been formed of pure polypropylene, the oven can be held at a temperature of about 1250° F. for approximately one hour to ensure suitable burnout of interior materials. Removal of the materials will leave voids within the hardened cast conforming to the shape of the precursors, attachments, and runner bars.

[0059] When the precursor material is burned out of the investment cast, it is possible to leave residue of the precursor material on the interior walls of the cast. The presence of residue can cause flaws on the final product. For example, residue left on the interior walls of the investment cast can cause flaws such as pitting on the final product. It has been discovered by the inventors that the use of pure polypropylene as the precursor material can enable more complete burn out of the precursor material and lower the possibility of the presence of surface flaws on the final product

[0060] Once the investment cast mold has been prepared as described above, the final product may be formed by casting a molten product material in the mold. For example, a molten gold alloy may be cast in the mold. The gold alloy used may be any one of several possible alloys, including 22 karat yellow gold, white gold, coin golds or other suitable gold alloys. Other materials may also be cast by this method, for example, other precious metals may be cast. Other precious metals which may alternatively be cast can include, for example, platinum or silver alloys.

[0061] The final product is formed by filling the investment cast mold with the molten material. It may be advantageous to use a machine specifically designed for investment casting to ensure a complete fill of the mold. There are many investment casting machines known in the art, such as those available from the Microstar Corporation of Norcross, Ga. One such casting machine is the KDF Cascom machine available from the Microstar Corporation. Another possible casting machine is the VarioCast machine, also available from the Microstar Corporation.

[0062] One possible embodiment of the present invention in which a KDF Cascom casting machine is employed to cast a gold denture tooth will now be described. A predetermined amount of the desired gold alloy is first heated in the main crucible of the main chamber of the machine to a temperature of about 1150° C. In order to be cast, the gold can then be heated to a higher temperature of about 1300° C. and held at that temperature for a preset amount of time, for example, the molten gold can be held at 1300° C. for approximately 20 to 30 seconds. After this time, the gold is ready to be cast in the investment mold.

[0063] Meanwhile, the hot investment cast can be removed from the oven after the precursor material has been burned out. The cast can be placed within the Cascom machine with the sprue directly over the crucible holding the molten gold. The top of the machine can then be closed and locked. Pressing the melt button can activate the machine's automatic casting process. Once casting is complete, the gold alloy within the cast can solidify and cure.

[0064] After the gold is cured, the cast can be removed from around the molded gold. If an investment material such as Beauty Cast is used, the cast may be removed by merely dissolving the material with a water bath. Other possible investment cast materials can require other methods of removal. For example, the use of a particular solvent can be employed to remove the cast from around the molded product material. The gold dental device, for example, the gold denture tooth, which at this point can still be attached to extraneous gold which filled the sprue, can be separated from any extraneous gold. For example, the gold denture tooth may be cut from the extraneous gold at the point where the gold which filled the sprue meets the tooth. The extraneous gold can then be recovered and remelted for use in another casting.

[0065] Finishing steps, such as polishing, marking, or minor shape adjustments of the tooth can be performed. For example, a tooth can be stamped with an identifying mark such as an identifying number or series of letters. Such a mark can be used for various purposes. For example, the tooth can be marked for inventory control purposes or alternatively to allow for easy identification should the tooth ever need to be replaced or repaired. After all desired finishing steps are completed, the denture tooth is ready for insertion into a denture or delivery to the customer.

[0066] The investment casting process of the present invention also allows for production of artificial denture teeth and crowns which may be decorated in an individualized manner. For example, gem stones, such as diamonds, sapphires, etc. may be inserted into an open faced crown or denture tooth.

[0067] This investment casting process may also produce design devices such as Accents®, which are gold appliques of various designs used to insert into denture teeth. Small devices such as Accents® may be formed to any desired shape. For example, the process could form letters, stars, or any other desired shape. Once produced, Accents® can be anchored in a denture tooth or crown of a contrasting color.

[0068] A denture tooth may also be decorated with a gold on-lay on an edge of the tooth. For example, the mesial, distal, or incisal edge of a denture tooth could be covered with a gold on-lay which has been produced by the methods of the present invention.

[0069] In addition to artificial teeth, other dental devices may be produced by this method, such as caps and space fillers.

[0070] Gold teeth produced by the method of the current invention are suitable for use with a denture or may alternatively be suited for use as a dental implant.

[0071] These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims. 

What is claimed is:
 1. A process for producing a hardened polymeric precursor of a dental device comprising: creating an injection mold, said injection mold defining a cavity of the shape of a dental device, said cavity having at least one wall, said injection mold comprising an insert, said insert being located within said cavity so as to maintain a gap between at least a portion of said insert and said wall of said cavity; injecting a molten polymeric material into said injection mold, said polymeric material substantially filling said gap; and setting said molten polymeric material to form a hardened polymeric precursor of said dental device.
 2. The process as defined in claim 1 further comprising producing an investment casting mold from said hardened polymeric precursor.
 3. The process as defined in claim 2 further comprising removing said hardened polymeric precursor from said investment casting mold.
 4. The process as defined in claim 3 further comprising casting a metallic material in said investment casting mold to form said dental device.
 5. The process as defined in claim 1, wherein said polymeric material comprises a thermoplastic material.
 6. The process as defined in claim 1, wherein said polymeric material comprises a polyolefin.
 7. The process as defined in claim 5, wherein said thermoplastic material is selected from the group consisting of polypropylene, polyethylene, and copolymers thereof.
 8. The process as defined in claim 1, wherein said dental device comprises a crown for a tooth.
 9. The process as defined in claim 1, wherein said dental device comprises a tooth.
 10. The process as defined in claim 4, wherein said metallic material comprises a precious metal.
 11. The process as defined in claim 10, wherein said precious metal comprises a gold alloy.
 12. The process as defined in claim 11, wherein said gold alloy is selected from the group consisting of 22 karat yellow gold, white gold, and coin gold.
 13. The process as defined in claim 3, wherein said thermoplastic precursor is removed from said investment casting mold at a temperature of about 1200° F. to about 1300° F.
 14. The process as defined in claim 11, wherein said dental device comprises a wall, said wall having a thickness of from about 0.0010 to about 0.0011 inches.
 15. The process as defined in claim 1, wherein said injection mold defines more than one said cavity.
 16. The process as defined in claim 2, wherein said investment cast comprises more than one said hardened polymeric precursor.
 17. A process for producing a unitary tooth comprising: creating an injection mold, said injection mold defining a cavity of the shape of said unitary tooth, said cavity having at least one wall, said injection mold comprising an insert, said insert being located within said cavity so as to maintain a gap between at least a portion of said insert and said wall of said cavity; injecting a thermoplastic material into said injection mold, said thermoplastic material substantially filling said gap; setting said thermoplastic material to form a hardened thermoplastic precursor of said unitary tooth; producing an investment casting mold from said hardened thermoplastic precursor; removing said hardened thermoplastic precursor from said investment casting mold; and casting a gold alloy in said investment casting mold to form said unitary tooth.
 18. The process as defined in claim 17, wherein said unitary tooth comprises a wall, said wall comprising a wall thickness of from about 0.0010 to about 0.0011 inches.
 19. The process as defined in claim 17, wherein said thermoplastic material comprises a polyolefin.
 20. The process as defined in claim 17, wherein said thermoplastic material is selected from the group consisting of polypropylene, polyethylene, and copolymers thereof.
 21. The process as defined in claim 17, wherein said gold alloy is selected from a group consisting of 22 karat yellow gold, white gold, and coin gold.
 22. The process as defined in claim 17, wherein said hardened thermoplastic precursor is removed from said investment casting mold at a temperature of about 1200° F. to about 1300° F.
 23. The process as defined in claim 17, wherein said injection mold defines more than one said cavity.
 24. The process as defined in claim 17, wherein said investment cast comprises more than one said hardened thermoplastic precursor.
 25. A process for producing a unitary tooth comprising: producing an investment casting mold from an injection molded precursor; removing said injection molded precursor from said investment casting mold; and casting a metallic material in said investment casting mold to form said unitary tooth.
 26. The process as defined in claim 25 wherein said injection molded precursor comprises a polyolefin.
 27. The process as defined in claim 25 wherein said injection molded precursor is of a material selected from the group consisting of polypropylene, polyethylene, and copolymers thereof.
 28. The process as defined in claim 25 wherein said injection molded precursor is removed out from said investment casting mold at a temperature of about 1200° F. to about 1300° F.
 29. The process as defined in claim 25, wherein said metallic material comprises a precious metal.
 30. The process as defined in claim 29, wherein said precious metal comprises a gold alloy.
 31. The process as defined in claim 30, wherein said gold alloy is selected from the group consisting of 22 karat yellow gold, white gold, and coin gold.
 32. The process as defined in claim 25, wherein said investment cast comprises more than one said injection molded precursor. 